In signal processing, a finite impulse response (FIR) filter has an impulse response of finite duration. Infinite impulse response (IIR) filters, in contrast, may have internal feedback and may continue to respond indefinitely.
FIR filters may have several useful properties: (a) They require no feedback. Hence, rounding errors are not compounded by summed iterations. The same relative error occurs in each calculation. (b) They are inherently stable. Because there is no required feedback, all poles are located at the origin and thus within the unit circle. (c) They can be designed to have linear phase (or phase change proportional to frequency) by setting the coefficient sequence to be symmetric. Such may be desirable for phase-sensitive applications such as data communications, crossover filters, and mastering.